Gear-cutting machine



L. l. EVANS.

GEAR CUTTING MACHINE.

APPLlcATxoN FILED Nov. 22, 1917.

1,384,558. A Patented July 12, 1921.

INVENTOR.

A TTRNM UNITED STATES PATENT OFFICE.

LEWIS J. EVANS, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSEELECTRIC & MANUFACTURING CO., A CORPORATION OF PENNSYLVANIA.

GEAR-CUTTING MACHINE.

Specification of Letters Patent.

Patented July 12, 1921.

T o all Iwhom t may concern.'

Beit known that I, Lnwis J. EVANS, a citizen of the United States, and aresident of Illlrinsbui'g, in the county of Allegheny and State ofPennsylvania, have made a new and useful Invention in Gear-CuttingMachines, of which the following is a specification.

This invention relates to gear cutting machines and has for an object toproduce a new and improved machine for eliminating inaccuracies incutting gears.

A further object is to produce a gear cutting machine in which adifferential mechanism is employed for compensating for inaccuracies inthe driving mechanism of the machine.

A further object is to produce a mechanism for counter-acting theinaccuracies by employing two driving worms or screws.

These and other objects are attained by means of a machine embodying thefeatures herein described and illustrated in the drawings accompanyingand forming a part hereof.

In the drawings, Figure 1 is a diagrammatic plan view of a table anddriving mechanism of a gear cutting machine embodying the features of myinvention.

Fig. 2 is a diagrammatic view of a modification of the machineillustrated in Fig. 1.

In cutting or bobbing gear teeth it is customary to mount the work on arotatable table and to rotate it at a uniforms'peed as a helicalrotating hob or cutter cuts the teeth. The table is ordinarily driven bymeans of one or more worms which mesh with a master worm wheel securedto the table or t0 the spindle of the machine. It is essential that boththe worm and the worm wheel be accurate as to the pitch and the shapeo-f the teeth, as any inaccuracies in either will occasion an inaccuracyin the work, unless some means are provided for compensating for, orcounteracting, these inaccuracies. In carryingv out my invention, Ipreferably employ at least two worms for driving the table and drivethem in such a manner that the inaccuracies of one compensate for orcounteract the inaccuracies of the other.

In the drawing I have diagrammatically illustrated in plan view thetable 5 of a gear cutting machine. As illustrated, the table is drivenby a duplex driving mechanism which includes two driving worms 6 and 7meshing with a worm wheel 8 on the rotatable table. One worm is locatedon one side and the other on the other side of the table. The worm wheel8 is formed on or secured to the table 5, and it will be understood thateach worm may mesh with a separate gear wheel mounted on the table. Ihave illustrated such a construction in Fig. 2. The Worms 6 and 7 aremounted on parallel shafts 9 and 10, which extend beyond the table 5 andare operatively connected together and driven by two cross shafts 11 and11 and a differential gearing- 17 which operatively connects the shafts.The shafts 11 .and 11 are axially alined and a set of bevel gears 12operatively connect the shaft 9 to the shaft 11, whereas a set of bevelgears 13 operatively connect the shaft 10 to the shaft 11.

Power is transmitted from an outside source to the cross shafts 11 and11 by means of change gea-rings 14, a shaft 15 and a gear 16, which ismounted on the shaft 15 and which meshes with an external gear 18forming a part of differential gearing 17.

The differential gearing 17 may be of any type, but as illustrated, itconsists of the external spur gear 1 8, inside of which small bevelgears 19 are mounted so as to mesh simultaneously with bevel vgears 20and 21 rigidly mounted on the cross shafts 11 and 11 respectively. IViththis arrangement one of the cross shafts may get ahead or lag behind theother. The driving worms 6 and 7 may mesh lwith the same master wormwheel or a separate worm wheel may be provided for each, as abovestated, and illustrated in Fig. 2. In the latter case the two wheels arepreferably cut together and are placed one above the other and spacedcircumferentially 180 apart in reference to the position in which theywere cut. This arrangement causes any inaccuracies of one wheeltocounteract or compensate for a similar inaccuracy in the other wheel byreason of the cross shafts 11 and 11 and the differential gear 17. Forexample, if one worm drags slightly, due to the inaccuracy in the wormwheel or worm, the other worm will be speeded up a corresponding amountdue to the action of the differential .17 ,so that the resulting speedof the table 5 will remain substantially constant. It will, of course,be understood that the variations will be slight and that thedifferential 17 will tend to divide the error in each case so that theuniform rotationfof the table 5 is maintained and gears of maximumaccuracy are produced by the machine. `The duplex drive illustrated willtend to eliminate errors, whether the driving worms mesh with the sameworm wheel or with separate worm wheels.

From the above, it will be apparent that similar portions of the twosimilar worm gears are relatively displaced circumferentially and thatthe worms are relatively displaced circumferentially of the worm gears.

While I have -described and illustrated but two embodiments of myinvention, it will be apparent to those skilled in the art that variouschanges, modifications, additions and omissions may be made in theapparatus described and illustrated without departing from the spiritand scope of the invention, as set forth by the appended claims.

What I claim is:

p 1. In a gear cutting machine, a rotatable work holding table, at leasttwo worms for driving said table, driving means for both of said worms,and differential means operatively connecting said worms for allowingequal and opposite variations in speed between the two worms, wherebythe inaccuraces of one drive are compensated for by the other drive.

2. In a mechanism for producing uniform rotation, a driven means, atleast two drivingl wormstherefor, driving means for the worms, and adifferential device connecting said driving means for compensating forinaccuracies 1n the power transmitting relaspeed in one drive causes anequal and opposite variation in speed in the other drive.

4. In a gear hobbin machine, a rotatable work holding table, duplexdriving means for rotating the table, a rotatable cross shaft connectingsaid driving means and transmitting powerI thereto, and a differentialmechanism on said shaft through which power is transmitted t0 said Shaftfor reducing errors due to inaccuracies in the driving means.

5. In a gear bobbing machine, a rotatable work holding tabler at leasttwo worms for driving said table, a cross shaft for driving both worms,and adifferential gearing on said shaft whereby a variation in speed ofone worm will cause an equal and opposite variation in speed of theother worm.

6. In a gear hobbing machine, a rotatable table, similar worm table andhaving simi ar portions displaced circumferentially, driving worms forthe worm gears relatively displaced circumferentially of the worm gears,and differential driving means for the worms.

In testimony whereof I have hereunto subscribed my name this 21st day ofNovember,

LEWIS J. EVANS. Witnesses:

C. W. MCGHEE, M. B. GORDON.l

ears carried by the

